Antitumor agents, such as 5-fluorouracil, cisplatin, irinotecan, docetaxel, a combination drug containing tegafur and uracil (product name: UFT®), a combination drug containing tegafur, gimeracil, and oteracil potassium (product name: TS-1®, hereafter, a preparation containing tegafur, gimeracil, and oteracil potassium at a molar ratio of 1:0.4:1 may be referred to as TS-1), are clinically applied in chemotherapy for advanced gastric cancer.
Meanwhile, regarding postoperative adjuvant chemotherapy for gastric cancer to prevent recurrence or metastasis after resection of gastric cancer tumor tissue, a phase III study ACTS-GC involving over 1000 patients showed that the administration of TS-1 significantly prolonged survival time both in overall survival and in relapse-free survival compared to that of the surgery-only group, and had no problems in terms of safety. Thus, the administration of TS-1 is now recognized as a standard therapy in Japan (Non-patent Literature 1).
Although postoperative adjuvant chemotherapy for gastric cancer has been intensively developed as described above, the therapeutic effect thereof is not satisfactory. In addition, since it is largely due to genetic factors of patients whether postoperative adjuvant chemotherapy is effective, there is a problem such that it is not known whether postoperative adjuvant chemotherapy is effective until an antitumor agent is actually administered.